Asda is in consultation with staff and unions over proposals to “streamline” the contracts of hourly paid staff, which could leave around 3,000 workers worse off.

A spokesman for the supermarket chain said up to 60,000 hourly paid staff could be affected by the changes. These would see the basic hourly rate increase to £9 an hour but would see staff “forgo paid breaks” and class bank holidays – other than Christmas, Boxing Day and New Year – as “normal working days”.

The spokesman said Asda believed the changes, if they went through, would “make 95% of colleagues better off overall” and that the retailer would do something for the 5% of those who could be left worse off by the changes.

“We recognise that not all colleagues are going to be better off if this is agreed – 95% we believe will be, but 5% won’t be, and we will do something and make sure that there’s a transitional payment. What form that will take is what we’re trying to agree with GMB and colleague representatives at the moment,” he added.

However, Gary Carter, national officer at GMB, the union for Asda workers, called on the business to “stop this approach and negotiate the changes with staff properly”.

He said a similar contract to the one being proposed was offered on a voluntary basis to Asda staff two years ago and “nearly 60% of employees opted not to go on the new contract”.

“These contract changes will affect nearly 60,000 members of staff and they cannot just be imposed from the top,” Carter said. “Absolutely nothing has been agreed with GMB and we will fight any imposition of these contracts on our members.”

The Asda spokesman said the changes were being proposed in order to “streamline” contracts.

He said: “In any given store you could have colleagues working on five or six different contracts, potentially. Different rules, different terms – and that makes it exceptionally hard for a store manager to manage that. We’re trying to streamline it down and that’s also going to be better for the customer too”.

Asda said the proposed changes to hourly rate contracts – which would also see night-shift workers paid slightly more per hour but work shorter shifts – would come into effect in late 2019, if agreed.